The invention relates to a process for coating a substrate surface with a layer of inorganic material, which is vaporized in a vacuum chamber evacuated to 10.sup.-3 mbar or less by bombarding with an electron beam from a high voltage electron-beam gun and deposited on the substrate surface. Within the scope of the invention is also a device for performing and applying the process.
Problems of electrostatic charging arise while electron-beam coating substrate materials that do not conduct electricity. These problems are due to the fact that the electrons from the electron-beam gun are not conducted off in a definite manner, this because the electrostatic charging cannot be led off the electrically insulating coating and substrate materials nor from the coated walls of the vacuum chamber which also become insulating after a certain time.
The charging phenomena express themselves e.g. in non-uniform focusing of the electron-beam, in non-defined alignment of the beam as a result of non-defined electrostatic fields and in charging of the substrate material which, especially when coil coating plastic films, can lead to considerable coiling problems. The electrostatic charge can also lead to pinholes in the film as a result of discharging. The build up of the electrostatic charge can also lead to overlapping of the film.
Known from the European patent document EP-A-0545863 is a process of the kind discussed above, in which a low energy, ionizing electron-beam forming a plasma is passed through the gas phase of inorganic material to an anode. The resultant gas discharging leads to removal of the electrostatic charge. The disadvantage of this mentioned method is that a second electron-beam gun has to be housed in the vacuum chamber.